This is the second alpha of Blender 2.5. 2.5 is getting better each day. The new mesh editing project with NGON support seems to almost be ready for the upcoming beta2 release as well.

Quote: What to Expect * Big improvements - The 2.5 alpha 1 release has 100s of essential fixes compared to the alpha 0. * Missing/Incomplete Features - Although most of it is there, not all functionality from pre-2.5 versions has been restored yet. Some functionality may be re-implemented a different way. * Bugs - We've fixed a lot lately, but there are still quite a few bugs. This is alpha software, we're still working on it! * Changes - If you're used to the old Blenders, Blender 2.5 may seem quite different at first, but it won't be long before it grows on you even more than before.

Blender 2.5.2 is out now, that fixes some urgent bugs in the 2.5.1 release.