I have a 20" monitor. I have been looking at 24" & 27" monitors. I play mostly casual games from BFG. Is the 27" monitor an overkill? How are the newer games playing on wide screen?

I don't think it at all overkill. I have a 32 inch TV/Monitor on my main computer and its just great for gaming. I kinda grump when I am on one of the other computers we have with the smaller monitors. I found the cost of the 32 inch was very close to the smaller ones. You need to ask if the one you consider is multi-use for TV or computer. I bought mine at the local Office Depot.

Go for it !!!!!!!!!!!!!!

As for how the newer games play, it all depends on what resolution the game is in. It may appear in the middle of the screen with black on either side if the game is in a lower resolution. If you "stretch" the picture to fill your screen, it will make you completely dizzy to see everything all distorted! My monitor has a setting to auto-adjust to a game resolution and then back to the native resolution when I exit the game.

Desk space is also a consideration. A 22" or 24" is perfect for my space.

Look at monitors the size you are considering in a store. Consider how far away you'll be sitting from the monitor and what feels comfortable for you. 27" may be fine for you, but it might also seem a little too wide, at least at first.

On the other hand, if you're going from a 20" squarish monitor to a 24" widescreen, you may miss the vertical space of the 20" even though you have more horizontal space. So you just have to look at the monitors and judge for yourself.