miquell,
I'll try to suggest just 4 games to you (and with price for boxed set around $15 on ebay). I think that my "style" for games is like yours.
X-Men 2: Clone Wars
Comments: Technically superb. Great graphics, sounds and gameplay. You should buy this one! The soundtrack is techno (I don't like techno), but is composed by Kurt Harland, of Information Society and sounds really good.
An ebay link: http://cgi.ebay.com/BOXED-SEGA-GENES...item3356299268
Super Hang-On
Comments: The arcade mode is the port of the excellent arcade hit, by the master Yu Suzuki. The original mode is a career mode. Many people complains about the "delay" on the controls in this mode. But this happens because your motorcycle is a crap in the beginning. Try it for some hours in Kega Fusion and you will love this. This game is one of the few Genesis racing games that have in racing music + sfx + engine noise. Sounds reall good. And is very cheap on ebay.
An ebay link: http://cgi.ebay.com/Super-Hang-On-Se...item563ee29321
Two Crude Dudes
Comments: An exclusive port from the Data East's arcade. A bizarre themed beat-'em-up that you should have in your collection. The port, IMO, is arcade superior 'cause the gameplay is much better on Genesis. A lot of fun and a good partner for your Streets Of Rage II.
An ebay link:http://cgi.ebay.com/TWO-CRUDE-DUDES-...item53e39eebbd
The Revenge Of Shinobi
Comments: A true classic-masterpiece for Genesis. For many gamers, the best soundtrack ever (it's composed by Yuzo Koshiro). A must have. Some people could argue that Shinobi III is a better game, but as you said how much you care about the sound, I think you should go with this one. Very well drawn stages and great gameplay.
An ebay link: http://cgi.ebay.com/REVENGE-SHINOBI-...item58898b400a

