I've been wondering whether to get this or not especially with SFIV coming out next month. I'll most likely not touch it after I get SFIV. So is it worth it if I only play it for a month?

If you're gonna do online immediately then yes you need every ammount of training you can get. but if you're just gonna take your time and play only with your friends that are of similar skill level (or just don't mind getting raped), it can wait. For me I got it to tide me over til SF4.

personally i would see if the SFIV uses the same net code as sfII hd remix, just because its the same company putting it out, its a different team and i just hope to god they use the netcode from sfII hd remix because people are saying its the best netcode for online fighters to date! if its even a step behind sII HD (easier to type over and over) i might consider not getting sfIV and wait for the psn version to be released in europe instead!

Two different games, two different fighting systems, even if 4 lends heavily from the download game. Get it if  your a big fan of the original. Getting 4 eventually should not put you off, you may want to indulge in the polished SF2 experience from time to time.

Actually SF4 is not completely different as their entire philosophy for it was to keep the simplicity of SF2.
Definitely pick up SF2THDR, really worth it if you like the series.

I didn't think I'd get into it, but now 200/200 points, 150+ ranked matches and plenty of player matches later it was well worth my $15.  Plus it got me insanely pumped for SF4.

According to Ryan Scott ST2THDR is superior to SF4.

Can't say myself as I've only played the one of them but damn it's a good time.