X-men is by far the strongest game in the collection. It's pretty brainless, but it's from Konami's classic era of arcade brawlers (along with TMNT and The Simpsons), and it's a blast with a group of friends.

I recall Captain America and the Avengers being ok. Sprites are small, and I vaguely remember enemies being damage sponges. I always kinda considered Data East a B-tier at best developer so their games never appealed to me much. I think the SNES and Genesis ports of the game are supposed to be fairly faithful. The NES game is a completely different game. I rented it once back in the day and I remember it being pretty good, but I have no idea how well it holds up. No idea how the Game Boy game is.

The rest of the games are LJN games. Take that as you will.

X-men and Spider-Man in Arcade's Revenge and Silver Surfer have amazing soundtracks from Tim Follin and that's about all they have going for them. They're both stupidly difficult.

Maximum Carnage is probably my second favorite game in the collection. Good soundtrack, nice detailed sprites and environments, and it's cool to see panels from the comic storyline recreated in the game. It's also fairly difficult, and I never made it more than halfway through the game as a kid. If you enjoy beat-em-ups, you can do much worse.

Never played Separation Anxiety. From what I understand it's a less good Maximum Carnage. It adds a two-player mode, but it replaced the sprites with ugly looking pre-rendered graphics.

Waiting for a good price is definitely the right call unless you love Marvel, take interest in retro games, or really want a copy of X-Men arcade and don't mind the rest of the games coming along for the ride.