Hm. Well, alright, I'll try...expanding this to systems I've read would be a lot easier than ones I've actually gamed under, but I'll see what I can do...you DO get a better sense of the mechanics by actually playing, which I think I'll expand on a little on the second one, unless I change my mind. (Women can do that, y'know. Little known fact, men can, too. Or maybe we can't. Heh heh.)
Okay, for one that I liked...that, of course, is the hardest. I'm not an anti-mechanics type, but I AM a tinkerer. I tend to see game rules like tinkertoys...I don't always so much make new ones, but I DO tend to build new shapes out of them. I'm just lucky that my GM likes most of the suggestions I make. (Heck, she asks for most of them. "Dear, make the failing rules work." "Hon, when you've got a moment, could you put together a system for mirror magic?" "Take the trash out, dear." Well, okay, the last only applied to fixing Shadowknight, but...)
For one that I liked, I think I'll go with Earthdawn (1st Edition). I have to admit, my actual play-time experience with the game was limited, and I liked the *game* enough that it may be coloring my memories of the system, but I think it had a certain elegance. It was complicated enough to be fun to `play' with, but started running pretty smoothly with only a little practice. A bit clunkier dealing with spellcasting, but I think that would have smoothed out if the game had gone another session or two. It gave us a chance to play with all the funny little dice, but without having to roll double-handfuls the way you do in some games. {I liked Deadlands for the same reason.} The mechanics were absolutely built in to the gameworld...I can't remember now if Meera wanted me to port the Earthdawn system into another world, or if she wanted me to port the world into another system, but she asked me to do one of those, and I couldn't separate them. Their Steps and Threads are too interlocked with the concepts behind the Adepts and their underlying magic structure.
Couldn't tell you how easy it is to GM, though I didn't think it would be too bad. From a player standpoint, we had a little trouble with the GM giving people the choice between rolling our characters up on dice, or using their point-based system; the die rollers *all* came out significantly higher `value' (enough to be frustrating even in a friendly game), and I only suspected a couple of them of cheating...but as mechanics flaws go, that one's almost depressingly easy to fix. We had a roomful of experienced gamers new to Earthdawn, and the system didn't slow us down much at all... except, as noted above, when it came time to cast a spell. Even there, though, while we were going to be referring to the book for a while, we figured it out easily enough it barely interrupted gameflow.
As for indifferent, I'm going to go with In Nomine, and yes, I'm picking it a lot for that point above about playing-experience making a difference. I LIKED In Nomine's rules, right up until I tried using them for anything. The d666 system was cute and sounded functional, but...everything was weighted to the expectation of people playing Angels and Demons. Which would be fair enough, that being most of what the game was for, but they HAD rules for playing lesser beings, and even if they weren't PCs, they were certainly supposed to be around. Bluntly, the rules were broken just among the Celestials. Once a human came within 100 feet of them, the system was irrepairable. It supported the game in a gimmicky kind of way, but not past that.
Character generation was fun. If you think for a moment they gave any thought to having balanced characters, a quick skim through the GURPS adaptation will dispell that handily. One kind of Demon can imitate an Angel's powers...another kind made *really good* lasagna. (Okay, their front story showed a good use for this, but it's still a pretty limited power compared to many.)
I spent some time on the In Nomine list, especially as I was getting partly out of Amber. Time on ANY list is a good way to learn exactly where all the rules were broken. The In Nomine list was very busy. To play or GM... I don't know. I had fun, but I don't mind workarounds, and Meera doesn't mind ignoring the rules altogether. We rolled occasionally to see if there was an Intervention, and otherwise went mostly diceless. One of my all-time favorite characters was for In Nomine, and that game had a bad GM (NOT Meera), as well. But the system was undeniably broken, and broken in ways that broke the world in some places, too. Too simple a system for too complicated a concept, I think...but I have to say, the idea of playing it in GURPS sounds...awful.
As for a bad one... *sigh* I hate to go for the example I think everyone's going to pick, but of games I've actually played, I have to say, Amber. The diceless concept is fine. (Actually, that's not entirely true; I DO have a problem with diceless. Not playing it, but the idea of publishing it. There are several 200+ page books out there that say, "Make it up as you go along." It bugs me. But playing it is fine, especially with some of the GMs Amber's attracted - and I DON'T just mean Meera.) So what's left, of course, is the character creation rules...if you're using points, they should add up. Anyone who's ever played Amber knows they don't.
I like the Attribute Auction concept, actually, and I like the way people use it sometimes for `single-winner' auctions. The attributes you get from it don't work terribly well, and the ones picked for Amber are heavily weighted for a Throne War, but it works well enough with GMs who are using character descriptions more than numbers anyway. I still do like the idea of starting out with a couple rounds of poker even before the Auction, just to make things even worse.
After the Attributes, where the points are officially weighted to mean, "However important it is to the players," we jump to heavily priced Powers, and from there to comparatively underpriced Items, and then on to the completely free skills for potentially very old characters...and you pretty much might as well not have bothered. I suppose the points help people think about their character - maybe having to give some things up, not actually play Merlin. It IS, to me, an improvement over the games that really DO just say, "Ok, describe your character, and if it's OK with the GM, go for it." Amber at least has enough structure that I can sit down and make a character without having to bug the GM every five minutes with, "Is this OK, too?" But if the rules WORKED, then everyone who plays wouldn't have their own. They can't support themselves, let alone the setting...and just don't get me started in Shadowknight.
Okay, and for the final part of the question...um, let's see. I'd like to try Immortals; once I *found* the rules in it (1st Edition), they were interesting, seemed pretty workable, and supported the game concepts much the same way Earthdawn's do (you couldn't use Immortals' dice system without Motes.) I'd like to play TORG, too. (I've been in a TORG game, but it was over a BBS, so I didn't get to use the mechanics much.) Ironclaw, actually, had an interesting way of using the dice - from reading it, I strongly suspect it's broken, but I'd still like to find out. It's tough to get me to say I wouldn't play something, but I'd play almost anything else before Over The Edge. Haven't been able to get hold of 4th edition Talislanta yet, but I know the older versions had great ideas...for *other* games. Otherwise, heck...I even play Amber.