I have played over 20 hours of multiplayer, and about 2? of singleplayer. Basically, I just got to the Nexus.
On the basis of that experience:
- The combat model is great, fun, challenging, and allows for a lot of customization. The multiplayer is a straight-up upgrade of ME3, though desperately needs some balance patches. However, with the state of the singleplayer criticism I'm not expecting them terribly soon. Mostly, the guns feel like water pistols. There are a few standouts (none of which I have unlocked), but for the most part the reaction on weapons in multi is one of "meh." Several of the powers could also use some buffing.
- I can see why people treated the game so harshly on the basis of the early singleplayer, because I am left overwhelmingly with the hope that it gets better. Most of the dialogue and accompanying animations are decent rather than spectacular, but there are some truly awful examples of animation and dialogue that stand out and leave you wondering if BioWare actually played their game.
- Speaking of things that make you wonder if BioWare played their game, I can't help but think nobody bothered to ever play the opening sequence of the game on Insanity using any sort of fragile character build, because that is easily the best way to determine the Save system is ****ING ATROCIOUS and the person/people who decided how priority saves work should be taken out back and shot repeatedly with their own underpowered multiplayer weapons. Implementing a checkpoint-only save system in a game where you have large sequences of exploration, scanning, and dialogue between short sequences of unforgiving (at least on Insanity) combat is idiocy. Alternatively, they could have had the decency to checkpoint BEFORE and AFTER each of the fights. Instead, the opening sequence took me three times longer than it needed to because I spent many minutes repeating all the same exploration steps between fights (level 1 charge and Insanity don't get along very well, especially after multi with a level 20 vanguard). Every major RPG over the last 20 years has had a quicksave, and why BioWare couldn't be bothered to implement it here is beyond me (especially considering the immersion-breaking nature of the manual save when the game does allow you to do it).
I've only proceeded this far in SP in order to be able to "cash" rewards earned in MP, and I'm hopeful there will be some patches before I leap into SP more fully down the road. I mean, it's BioWare so it's still better than a lot of other content out there, but it definitely has problems.
All that said, there a some decent discounts on the game now and multiplayer is a ridiculous amount of fun, so if anyone is in the "not sure but I'd really like to coop again" camp, I'd say pick it up.