I had the Kross 2 88 but sold it some time ago.
Sound and function wise, I didn't have much to complain about, but ultimately, a workstation wasn't what I wanted and the action fell short for me. Don't get me wrong, it's not a bad action, more or less comparable with Yamaha's GHS, although the latter is a tad better for piano.
If you want to buy the Kross 2 88 as a controller to play pop and rock music, then I don't think you'll be disappointed ; the NH is solid enough for that, unless you want to go play more advanced classical pieces.
If you can get if for more or less the price of the 61, then I wouldn't hesitate, really (I actually got mine for the exact same price of the 61 ; whether that was a mistake on the website or intentional, I don't know, but the price went back up a few days after I bought it, and I actually sold it with a bit of a profit

)
For the rest, Biggles already summed up the pros and the cons, so I guess you get the idea. I just wanted to comment on the action specifically since I know Biggles had the 61 key model. Just wanted to add that the higher-end action from Korg is not the PHA4 (that's actually Roland's), but the RH3, which you'll find in the (amongst others) D1, SV1/SV2, Grandstage and of course the Kronos 88 and that keybed is actually really really nice.
The NH is, as was said, in the B1/B2, the XE20, Kross 2 88 and the Krome EX 88 (amongst others).
If you actually need all the functions that come with the Kross 2, then by all means, go for it. If you're just looking for a controller, the D1 is more 'bare bones', but is probably even cheaper than that Kross 2 88 on sale, and the keybed really is miles ahead. Just a thought...