We're quite a way into the lead-up to Infinite Crisis, so without actually going back and re-reading the miniseries and tie-ins up to this point, these are my opinions off the top of my head.
The OMAC Project: Five issues in, and this remains my favorite of the minis. There's some great action, a good mystery, and enough suspense to keep me wondering what's going to happen next. The only problem I really have (besides the wholesale slaughter of JLI members) is that there's no way they'll be able to wrap up the story in the next issue, and it'll just bleed right into the Infinite Crisis miniseries.
Day of Vengeance: This story finally hit its stride, though it seems a little too late. We know very little about some of the principal characters (i.e., Nightmaster), and the long Spectre/Captain Marvel battle seems to have had little importance in the long run. This series has alternated between fast-paced and plodding, with the only common factor being the ever-witty dialogue and the fascinating cast. It's not as bad as I'm making it sound, but it's not my favorite series. Maybe I'm just wary of the "destruction of magic." Oh, and kudos to Willingham for finally characterizing the Spectre.
Villains United: Easily the most fun miniseries, I certainly hope some of the main cast members of this book translate into a new Suicide Squad. Cheshire's baby with Catman (if nothing else, a nice play on their respective codenames) is a neat angle, and I like the idea of idealistic antihero Catman being perceived as a sort of Batman-wannabe, which would further underscore his past relationship with former-Batman-wannabe Green Arrow. Simone's dialogue is top-notch, and the banter between the supervillains on both sides is fantastic. OMAC's my favorite for action, Villains is my favorite for characters.
Rann-Thanagar War: And R-TW is the forgotten red-headed stepchild of the bunch. I love the characters, particularly the Hawks, Kyle Rayner, and Adam Strange. I only have a passing familiarity with the Omega Men, Captain Comet, L.E.G.I.O.N., and Komand'r, but I recognize them all. I'm even a bit familiar with Onimar Synn. So why does this series leave me so confused? Is it because I don't recall the individual events of each issue from one issue to the next? I'm not totally sure. I expect this to make a lot more sense when I can read all six issues in a single sitting, but so far it's a jumbled mess. Considering that it spun out of the exemplary Adam Strange miniseries, that's a shame.
DC Special: The Return of Donna Troy: Hey, look! Donna Troy's screwed up again! When you go through origin stories, costumes, and powers the way other people go through socks, it's bound to mess you up in the head. Just look at Henry "Giant Man/Ant Man/Yellowjacket/Whatever else" Pym. I bought the "Who is Donna Troy" trade in hopes that it would make some sense out of all of this. Who was I kidding?
Sacrifice: I posted my feelings on Sacrifice before, but here's the short: the first two issues are unnecessary, Adventures and Wonder Woman are a pretty good read, and it all should have been nicely recapped in OMAC #4. But, easily one of the strongest tie-in stories outside of the miniseries.
JLA: Crisis of Conscience: You know, I don't care what your personal feelings are for Infinite Crisis or the Identity Crisis fallout, the fact is that this is the best JLA story arc since Joe Kelly left as the regular writer. After the hackwork of Claremont and Byrne pimping the latter's continuity-mangling Doom Patrol pap, and then the hackwork of Chuck Austen's moody, continuity-ignoring depressed-hero garbage, then the worst thing I've ever seen from Kurt Busiek, a convoluted, boring, anticlimactic story that couldn't reference half of the crossover it followed up on, after all that, it's nice to see an action-packed, intriguing story featuring the Justice League and an honest-to-god supervillain or eight.
Teen Titans: Raise your hand if you're not buying the new issue! Two bad reviews + Rob Liefeld + hit-or-miss Gail Simone = Not worth my $2.50. Maybe the next time my comic shop has a sale, I'll pick 'em both up for half-price. But the issues before it were pretty good. I liked the Superboy story stuff, and it was nice to see the fallout in Superman, where the Man and Boy of Steel commiserate over being mind controlled (less nice was the resurrection of that awful soul-vision garbage). Titans hasn't been sucked into the full crossover mode, but the teens have been dealing with aspects of it, and dealing in interesting ways.
JSA: A nice lead-up to Day of Vengeance in the book that deserves it, since the Spectre is still a card-carrying JSA member. I guess Eclipso sort of is too. And it was nice to see an OMAC finally laid out flat, and to basically confirm that Mr. Terrific outsmarted Batman.
Batman: I'm skipping out on War Crimes, but I'll come back when they start talking about Red Hood again. Does this tie in more than tangentially to IC? Got me.
The Flash: Johns is one of the architects of Infinite Crisis, but his books seem divided. Teen Titans and JSA are pretty well-involved in the crossover, but Green Lantern is way off on its own, and the Flash? Is Zoom in the Society? I really haven't been totally sure. Either way, Rogues War rocks, and it'll be a bit painful to see Johns go. Although his run between Ignition and the war left a little to be desired.
Are other books tying in? I know there's a bunch of "red skies" issues, though people promised there wouldn't be. Ah, well. That's all I have off the top of my head. Oh, and incidentally:
JSA: Classified vs. Supergirl: Geoff Johns is telling the origin story of a superpowered woman who may or may not be from Krypton, with a story that is full of heart, humor, and mystery. Jeph Loeb is telling the origin story of a superpowered young woman who may or may not be from Krypton, with a story that is full of battles and cryptic dialogue. Jeph, take a hint from Geoff. He does mysteries *much* better than you do.