Here's a short list. As always, feel free to add on.
COUNTDOWN TO FINAL CRISIS #03: A good Superman/Darkseid fight is ruined by some really bad Superman dialogue. I still shake my head at Mary Marvel going from 0 to 60 in terms of evil in the blink of an eye and it has me thinking she'll bite the big one during Crisis. And yes, as we all suspected but didn't want to believe, the big payoff to all of this looks to be Jimmy Olsen vs. Darkseid. I waited a year for THIS? Thumbs down.
BOOSTER GOLD #8: The exposition regarding Max Lord still makes me sad, if only because now you can't really read the classic JLI the same anymore, especially since they try to convince you that Lord was evil from the very beginning. Other than that nitpick, this is a great issue and I'm loving the evil time travelers (though Despero looks awful). Definitely come back for more next month if you're a fan of the old JLI. Thumbs up.
FANTASTIC FOUR #556: Ehhhhh, this probably wasn't a good jumping on point. I'm wondering if this'll read better in trade. It wasn't actively BAD, but it just didn't work for me for some reason. Maybe because Reed was almost totally absent. I'll likely sit the rest of this one out and pick up the trade, because I love the Millar/Hitch team. Thumbs squarely in the middle.
AMAZING SPIDER-MAN #556: Got hooked up with this one by a friend trying to get me back into Spidey and give BND another chance. It's not working. I've seen enough "Oh noes! No webbing!" cliffhangers to last me the rest of my life. This isn't exactly breaking new ground. Maybe things get better in August when the T-bolts show up. Until then, it's another thumbs down.
DELAYED EDIT: I'm reading the IGN Comics interview with Geoff Johns, who notes that the Despero in Booster Gold is actually the original Despero from his first JLA appearance, which actually explains his character artwork. I rescind the previous comment.
I've actually enjoyed the last two issues of ASM. The art is about a million times better, and the story seems to be doing what the previous writers were trying (and failing) to do, which was harken back to some classic, basic Spidey stories. Now, I'd sell my own mother for a JMS Spidey miniseries, but failing that, the last few issues have been an acceptable, if bland substitute.
"I could drown the pain, and drink upon commuter trains, and here you stand in eastern standard time" - Mike Doughty
I thought Flash#13 was good for what it was, but it's unfortunate that the Powers That Be at DC decided the character of Bart Allen needed to be sacrificed (seemingly). I think there is a bit of wiggle room with Inertia involved, but who knows?