I'm having a ton of fun with the game. I also haven't touched SP yet. Been playing it during most of my free time since release.
Yes, Battlelog is shit. I haven't have a lot of problems playing because of it, but it's still a pain in the ass. It's an unneeded layer build on top of Origin (which itself is an unneeded layer). I like how when someone opens Origin, I get a popup telling me, then when they open Battlelog, that tells me they're online too. I'm not even sure the 64 player battles make it worth dealing with Origin and Battlelog, and I still wish I had gottent he game on Xbox. It was a gift from someone who wanted me to play with them on PC though, so I can't really complain when it was free.
I did co-op once, but didn't like it much. It was like horde mode from Gears of War, but with less room to move around. We failed the mission because an enemy armor vehicle drove up to and right past the line of NPC HUM-V's. As soon as he drove past them, the mission was over. So basically we're tryign to hide out of line of sight of these dozens of guys coming at us, and then have to stop everything and take out the tanks/vehicles when they come or they just drive non stop toward your back line, and letting that happen is an instant loss.
So if you strip out the SP, the co-op, Battlelog, Origin, and just look at the MP game by itself, it's amazing.