I picked up Overkill a few weeks ago. Honestly, I don't think the new overkill mode is for me. Adding high-speed medals that home in on your ship, in a game with high speed bullets, is not a good combination. And why even have medals if you just autocollect them anyway? Also, while "overkilling" is cool when not much is going on, it's frustrating when I can't hit enemies for several seconds as I wait for wreckage to clear out.
I also don't like how charge-up shots were nerfed scorewise. Building up a huge missile salvo to quick kill a big enemy and watching it explode into bonus points everywhere is fun, but now it's worth so little why bother.
So in short, lots of new ideas that may be good ideas in other games but don't mesh well with Raiden style, while trivializing the part of Raiden IV I liked best.
That said, this package is still an awesome deal since you get the arcade mode and 360 mode, plus the dlc ships. The non-overkill modes are still great and I like them a lot.