I just got an Oxygen 88. I've been using it for a little while now, and I too have been looking for reviews. Not much exists. But I decided to get one anyway because it was the only thing in my price range that had exactly the features I wanted and nothing more.
So far it's a great thing. I've felt better hammer action keys, but the action on the 88 is pretty solid. My one gripe right now is that the black keys are a little light and kinda squishy when you're playing light, so those keys end up striking first when you're lightly touching a chord. Kinda makes you feel a little sloppy. And they also take a little more force to get upper velocities. Maybe I'll get used to it.
The ivories feel weighty though. The rest of the unity is solidly built. Plasticky kinda, but well made. The whole thing is pretty light, which isn't a bad thing. It doesn't feel remarkably expensive, but then again, it isn't.
It does have 3 on-board velocity curves, which are well balanced, but not extremely useful for me thus far. Lots and lots of MIDI assigning options that I haven't explored yet.
It's USB powered, which is awesome. No wall plug. And it has presets for mapping its transport controls and sliders to common DAWs, which is also a plus. So I can control the Pro Tools transport while I'm turned around at the keys.
I bought mine used from Musicians Friend for under $400, and I feel like I got a hell of a deal. 88 weighted keys, bunch of MIDI controls, USB, pitch & mod wheels, no frills. Exactly what I needed. Paired with a good piano library, it's a joy to play.