Ok, Mike, I'm going to try to answer all your queries.
1. No, there will not be a 3rd beta. The next will be RTM & GA, neither are betas, anymore.
2. There are absolutely NO UPGRADE paths from non-beta OS to betas nor from 1 beta to another nor from a beta to RTM or GA. The only time upgrade is OK is from 1 non-beta OS of a certain level to certain levels of another non-beta OS. 'upgrading' from whatever to the CP is wrong & same applies to the RP or any other beta OS. This same principle was true w/ Vista & Windows7... will always be the case.
3. I hear Classic Shell, still, works but, there is, still, no need for it & it, honestly, just confuses things, I'll say. Point is, Win8 can be very easy to navigate & find things (@ the Desktop) w/out adding any 3rd party means. The only thing I, actually, added is just a 'shortcut' that makes it so I can have (all) applications in a Taskbar folder. This put everything, not just what tiles are on Start, @ my fingertips w/out leaving Desktop.
4. As for "being stuck w/ it (Metro UI) on a big screen monitor", you are not (stuck w/ it)! I have a 24", non-Touch, desktop PC. There choice IS there to spend 99.999% of one's time & activities @ or from the good ole Desktop. Plus when I do look @ Start, I have the quantity & arrangement of the tiles such that I do not need to move the screen to see them all. Remember, just cus something is in the machine, there does not have to be a tile for it (kept) on Start. And, that same item can, still, be easily accessed whilst on Desktop.
5. Games - I can't see much, like Free Cell or Solitaire or whatever. There is a tile for Xbox games, some free. Also, > the Store tile & there are a number of free games available. And, of course, more in both that can be purchased.
6. There are a fair bit of 'new & improved' in the RP (or Beta2) from the CP. Some under the covers & or subtle & some more dramatic & obvious. It is, @ least, as fast as the CP, if not more so. There is no longer any need to add Flash, WinRAR or PDF readers. The corners work better to the mouse & things are better sizes. There are more choices for cosmetics, colour & pictures selections & so on. Also, many of the APPs are improved. There will be additional enhancements between this beta (the RP) & RTM. Remember, this OS is, still, a work in progress.
I trust I have come, @ least, somewhere near addressing your curiosities.