Trid: Are there any problem with GTA4 and GfWL now when they turned it off?
Also, did they somehow optimized it? Or it's as bad as it was on release?
From what i know the only problem is that multiplayer will be shut down once GFWL goes down. If i recall correctly, the game supports offline GFWL profiles, so there should be no problems with offline single player once GFWL shuts down, unlike Bulletstorm, for example, which requires an online profile (and we don't know what will happen to this game once GFWL shuts down).
Did they optimize it? Well, not so much. It's still pretty demanding for what it offers, but modern PCs should have no issues running it anymore. It's definitely not as bad as it was on release, for sure, but it's still a shitty port and nothing will change that.
You are aware that GTA 4 has 2 DRMs, right? It has SecuROM and Steamworks as DRM, not to mention that it requires both a GFWL and a Rockstar Social Club account. So, that's 4 annoying things for you. Also, there are people who have issues with that Rockstar Social Club crap. I haven't encountered any issues with it, but there are tons of threads on the Steam forum complaining about it, so, keep that in mind.
Do you have a console? If you do, i really recommend you get the console version instead of the PC port.