In terms if of level design and the general playability is concerned, 3 is very much indeed the best designed and built classic game out there.
while 7 has more production values, it wasn't nearly as well laid out and there is nothing special or creative from any of its levels. The art got better, the rush thing was very much improved. but the "search" item felt mostly tacked on.
there were maybe 3 times in the game you actually wanted to use the thing, and none of the items you could find were only though search.
as far as the X series ares concerned, imo, 2 and 3 are tied for best in X. The X series really started to suck the moment the made Zero a playable character full time. 5 > 4 > 8 > 6 > 7
yeah 5 was more fun than 4 was. 4 was loaded with instagib powers when you attack bosses, combined with the easiest fights and shortest levels. sure there are a few hard fights, mainly Dragoon, and 2nd form sigma (as zero)
but the challange just is not attached to any X post 2 really.
if ever they follow suit on a "retro" X9, they need to get rid of all the bullshit characters, and get back to X, and X only. Multiple armor upgrades, fine, but no more fucking axl. I can handle more Zero if they change him back to the way he was X/X2
as to underail, the 8bit mm7 game was is pretty good, played a bunch of the levels, but the only thing that truly irks me about it is the maximum of 2 simultaenous inputs.
(ie. charge+forward, jump+forward) not being able to charge, move forward and jump really sucks.
just imagine how much a game from today would suck if you could only do 2 things at the same time, but there are actually 8 or 9 buttons. (hell in metroid prime i can think of doing 6 things at once.. charge,run,jump,turn,aim/lock,shoot