I've played through JJA a number of times, though always with some time in-between, and generally enjoyed myself. I kind of like the health system, where you come back to life in the same place you die, but it's not made much of... it might have been cool to incorporate some of the style of Battery Check, so that the weaker you were the slower you were.

Combat wasn't too cool; weapons, despite their realism, were basically reduced to the level of JJ1 weapons, most behaving about the same way but with different degrees of damage. The ricochet gun should have been an exception but I never found any good uses for it in the level design outside of the targets; the flamethrower, though, was really cool and I applaud them for it. Carrot grenades were also pretty cool, although I'm not sure they deserved their own button and being generally separate from the guns.

The enemies didn't help with the combat because they were (nearly) all the same behavior, walking back and forth and attacking you with a set number of attacks, which is all the worse when you realize that all the bosses (except for King Chameleon, whom I also enjoyed) work the exact same way. It's just a matter of shooting them more than they shoot you, and some of their attacks are really hard to jump over. That said, I do appreciate games in which you and the enemies have (some of) the same attacks -- if nothing else it's a good explanation for why the ammo is there in the first place -- so that's cool.

Jazz's movement engine was probably the worst part of the game. I shouldn't say I wanted an exact clone of the JJ2 physics, but maybe I did -- as it was, jumping (and coptering) were entirely too hard to use, especially given how much control JJ2 gives you (see: any test level). And yeah, no running? What? The level design didn't help with anything: lots of small platforms and leaps of faith, coupled with bottomless pits and falls that hurt you (which addition I do like in principle, but it was misused), and as someone said lots of enemy clusters. The few moments the level got interactive -- switches, moving platforms, ricochet targets, disappearing platforms, the chameleon mouth -- I enjoyed it immensely, but in general the environment was about as basic as JJ1 but with different enemy behaviors.

All the thematic stuff I liked, with the obvious caveat that I missed all the characters who got lost. The plot is simplistic but that's not really a liability in a Jazz game. The store visits in-between planets are a good addition, and I appreciated both the new tilesets and the tileset remixes, particularly the pollution planet (and isn't it nice that Jazz is going to planets again?). It was also cool finally seeing ingame cutscenes, since neither JJ1 nor JJ2 really supported that in any way (the closest we ever came being the HH94 ending movie). I only ever played multiplayer once, I think, with Sal, so my experience is much too limited to have any opinion there.