Really enjoyable. The game will forever be compared to 4 (which is unfair as 4 was a classic, yet understandable considering it really is a sequel to 4 in regards to both gameplay and plot). Seriously though, if you loved 4, I don't see how you won't get a great deal of satisfaction from 5 (unless you're ridiculously nitpicky and petty). Coop is an absolute blast. I put 3 or 4 hours into the game solo, and still had a great time, but coop makes the game considerably more enjoyable in my opinion. If you get the game, you really need to make an attempt to play coop, even if it's just with random people over Xbox Live or PSN.
There are some really impressive graphics in the game, certain areas are amazing. If you're a graphics whore, you'll enjoy it (though there are admittedly some nitpicky areas that obviously got less time on the graphics than the rest). Regardless, I'd say it's sitting pretty close to the top of the list for having some of the best graphics of this generation.
The core gameplay is admittedly quite similar to 4, but it's all bigger and really fun. You'll get in battles with huge amounts of characters, or sections where you straight up have no idea how you're ever going to pass it when you first see what you have to fight. The "rail shooing" type moments in the game were actually incredibly fun and some of the most memorable moments (instead of terrible, like in a lot of games). There are some obvious differences in gameplay in regards to your inventory and how it's handled in real time between the two of you, but it all seems to work out well in the game, and actually makes the game considerably more "tense". This inventory system also requires you to actually "cooperate" with your partner (even if you're playing it solo with the AI partner), which makes it more enjoyable and immersive as well. The enemies are fun, varied, and fit the setting. The claims of the game being "racist" seem ridiculous now when you actually play it. The bosses are pretty jaw droppingly cool, and quite fun as well.....until the end. There were a number of boss battles in the last bit of the game that were straight up annoying in how you had to kill them. It's not that the method to do it was bad, it's that it takes you multiple times of trial by error until you figure it out. There were a few I don't think I EVER would have figured out what I was supposed to do without looking online or just getting lucky. Both of us were quite frustrated during the last 3 hours or so of the game, as the bosses turn more to the really bad side of Japanese game development with trial by error, confusing gameplay choices, too many cut scenes, and repeated "you think he's dead, but he's not really dead!" segments. Admittedly a lot of that could have been because of how long we'd been playing, but I imagine a large number of people will feel the same way towards the end. It just seems really anti-climactic to have an absolutely stellar game become annoying and lose its fun factor for the last 20% of the game. It'll be interesting to play through it again, as maybe I'll think it's fun now that I know exactly what I need to do.
A couple items to nit pick: overall "scariness" and controls. This game isn't remotely scary. It's very intense, and there are moments that get the blood pumping because you're "scared" that you're going to die or not get a way, but you're never frightened from atmosphere. There aren't even any cheap "jumpy" moments. Compare it to other recent horror games like Dead Space (which was obviously modeled after RE4) or Condemned, and there's a night and day difference. Sure, RE4 wasn't all that scary either, but still leaned much farther in that direction than this did. It doesn't hurt the game, but it's disappointing in comparison to how the series used to feel. You need to expect an action game, not a horror game. And that leads me to the controls. They're adequate, and work fine in the game, but they're friggin' dated at this point and it'd be nice if Capcom actually got off of their high horse and looked at big Western 3rd person titles for at least a little inspiration.
Don't let my gripes worry you too much. Overall, it's a blast and another great episode of a classic franchise. If you're a fan of the series (particularly 4), I honestly don't know how you won't have a hell of a good time with this. As always, Capcom put a ton of value in the game: Around a 12-15 game on normal difficulty, massive amounts of unlockables (weapons, costumes, graphical filters, effects, characters, abilities, etc), the ability to play through the game again on higher difficulties with your upgraded inventory (finally!), different modes (Mercenaries in online coop after you finish the game!), tons of back story etc. etc. etc. I'm already looking forward to playing through it again on a harder difficulty, and putting some serious time into Mercenaries mode.