When comparing Brawl and Melee: Melee was faster than the original. Many people didn't like that. When Brawl came out, they slowed the game down again, and that made it better IMO.
As to whether or not Brawl is a serious game: it is one of those easy to play and hard to master games. How do I know this? I played Melee with my friend quite a bit. When I sold it, it had 300 hours clocked into it. I would say I am an advanced player. I haven't met a single player (except for above mentioned friend) that can come anywhere close to defeating me. I simply manhandle them. In other games, like Soul Calibur and Mortal Kombat, experience helps. However, new people who button mash still do somewhat well. That isn't the case in brawl.
I did like Street Fighter II. I do plan on getting Street Fighter IV for the PC. However, if you are playing a traditional fighting game like that, you are better off with Tekken. I guess I am biased since I practice Martial Arts and like the more realistic approach with traditional fighting games.
