I'm enjoying it. It has a lot of replay value with collectibles/weapons/etc.
The story wasn't that great. I think Kojima and his crew spent ~9 months writing the script for MGS:R and when it was molded into MGR:R they spent 1/3 of that time on a new script. It's a shame Metal Gear Solid: Rising never came to be, a lot of people wanted to see what happened to Raiden between 2 and 4, and for now we just have to settle on the MGS Database and some text.
Most of the characters were fogettable, too.
The gameplay itself is a lot of fun (especially when you get new weapons/wigs/etc). I'm currently running around as Gray Fox w/ fox blade and wreaking havoc. I'm not disappointed in dropping $60 on it.
But, I'm definitely ready to drop $150+ on some Ground Zeroes CE and more info on 5.