More Thoughts on Crackdown and Zelda: Twilight Princess
Yes, oddly enough they're related. 
I wrote some thoughts earlier on Crackdown that were super-positive. Having played through and "finished" the main storyline as well as received quite a few of the achievements, I thought I'd give you a few more thoughts.
First, the game really is just that fun. It reminds me of the old days when you could hop into a quick shooter on the 2600 and just play for an hour or so. The sandbox world is wonderfully realized, and even as you head off and chase down different bosses you'll find yourself distracted by a missed orb, a great place to put a ramp truck, a huge collection of explodable things just begging to go bang... the list goes on and on.
That said, the game is not perfect. As you attack bosses you quickly realize they're really nothing more than a differently-named henchman with buffed-up health. It's still lots of fun finding different ways to get to them, but the actual end-fight is pretty anticlimactic. A couple of rockets or kicks and you're done. Targeting can be finicky, and sometimes you stay locked on a target that you just don't want anymore. And the majority of the music is disappointing; I like a few of the rave/ambient tracks in the Volk territory, but that's about it.
It would be unfair to say that co-op is the saving grace for the game because even if it hadn't been included you'd still have a ton of fun. The good news is that co-op does add yet another layer of replayability, and I just can't stress enough how much fun it is. But even there one wishes there were more cooperative requirements or objectives. While you can attack bosses together, there aren't any "co-op only" bosses or puzzles that would require you to coordinate and solve the problem. Some might consider that a strength (in that you can individually attack the world independently), but I'd love to be a little more closely-connected to my partner. There was a social intimacy when playing Splinter Cell cooperatively that Crackdown is missing.
But here's the funny thing - even though I can highlight areas I'd like to see Crackdown (or hopefully, a future sequel) improve, it's sort of crass to criticize the game. In the end it really does deliver an incredibly fun experience. I saw a blog post somewhere (which I can't find again unfortunately - please send if you know it!) where someone compared Crackdown to watching a Ninja jump a flaming motorcycle over the pit of death but being disappointed because the Ninja wasn't juggling. (Note that I'm not remembering the description correctly either, but you get the gist.) It's still an amazing experience, built on an firm base, and being able to experience it with a friend (game-design flaws and all) is a blast.
So how does this all relate to Zelda: Twilight Princess? Simply put, I think I'm done with it. I'm about half-way through Zelda and enjoyed what I've played of it. But when Crackdown came out it won over my time and I didn't even think about Zelda for weeks. Now that I'm "done" with Crackdown I could return to Zelda at any point - but I just don't have the urge. And when I try to analyze why, I realize it's for two reasons.
The first is simply that it's the same game I've played a million times before... it's good, but hasn't advanced in, what, a decade? And much as it pains me to say it, there are enough new experiences out there that I fear I may have outgrown Zelda as it exists today.
The second is that I realized that what would have brought me back to Zelda, as-is, would be the ability to play through with a friend. Just as Crackdown adds a whole layer of replayability thanks to its co-op support, being able to play co-op in Zelda would be absolutely magical. I think it could even hit that magical level of social intimacy Splinter Cell was able to achieve in cooperative play. I can only hope that future versions of Zelda will take that online, connected experience seriously. If so, I'll be back in a heartbeat.