Performance is poor, and changeable settings are pretty non existent. Resolution, render quality (low, normal, high), and texture quality (low, normal, high) are the only changeable options for graphics.
The game also attempts to estimate the amount of video memory it will use, and won't let you set it above the limit of your card. It seems to guess than no more video memory will be used between all settings on low, and all settings on max. The only thing making a difference is resolution. What if the game doesn't recognise the full amount of graphics memory you have? (known problem).
It's a poor console port which needs patching.
Installation required 40 minutes to install, then a manual update of Windows for Games - Live!. Signing into the Rockstar Social Club crashed the game on the first day (offline play only), and you MUST be signed into Windows for Games - Live! just to save / load single player. I have to quit the game and load from the last save point every time my internet disconnects. It eats through 4 GB of RAM, whacks a 2.66 GHZ dual core processor, and uses my 512 MB 8600 GT graphics card to it's full. The minimum requirements are daft. I'd like to see any system just barely meeting them even get 5 FPS.
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The issues are supposed to be addressed shortly in a patch. Steam are currently offering refunds on a case-by-case basis.