It's not incredibly awful, but there are better ports. It feels like an emulator running random arcade versions of these games.
I've had some awful disconnects during online matches. To my knowledge there's no way to exit an online match, so players still message you saying you're the "roach" because the match got disconnected.
I have played 3rd Strike in a Japanese arcade cabinet, on the Xbox 20th Anniversary, the Japanese PS2 version, and the digital port on PS3. This version feels good at times, so I can't say it's that awful. Some things feel better than others. I personally like the feeling the arcade rom gives off. I'm also not an expert on the different technical aspects of each one I've played.
If you aren't sure on what technical or changes in the coding then you won't be that disappointed. Yeah it's stupid online for Alpha 2 or the first 2 SF3 games wasn't included and you don't get the extra characters in Alpha 3 that were in Alpha 3 MAX. It feels incomplete that way.
SF3 2nd impact is fun, but I only had a chance to play it in arcade after 3rd Strike was out. Not having it online sorta sucks.
The sad part is is that Capcom wants this game to be the current way to play these games online. Otherwise you have to load up emulators or older consoles. I don't mind playing my PS2 port alone by myself, but this is where you'll get a match for 3rd Strike online.