I always liked the OD, but mostly when using Channel 2 with it's own EQ settings specifically as my OD channel. Then i could use the amp switching in my BOSS GT-10B to toggle the amp OD on/off via the individual Channel B jack instead of the huge MESA multi footswitch. I don't recall ever hearing an OD pedal that sounds nearly as good as the tube OD on the Titan.
I actually haven't used my Titan in a few months as I left the rock band I was playing in and am trying some electronica right now and while a lot of synth sounds totally badass through the OD on the MESA on the flip side even with the OD off I can't get the Titan clean enough when trying to push pure, clean synth through the amp (too tubey for some synth applications) so I'm running into a Peavey IPR1600 right now and, gasp!, the Titan has been sitting in it's SKB case unused.
But my recollection was the OD was seriously excellent sounding, tons of low end if you dial it that way, and in fact if you dial the bass EQ up too high with the OD cranked you can get some really low sub-bass rumbling, mostly when trying to mute your notes off, but I'm not the best player so it could be my technique there. But it's real, badass OD, not some clever gated fuzz so it's not a clean chop on the end of the notes. The OD sounded super excellent with a touch-wah in front of it. But like I said a few posts up it would eat quite a bit of other effects if you had serious OD dialed in. Not that I ever tried it, but I would expect the same behaviour from sticking an OD/fuzz pedal at the end of your effects chain, so it's no fault of the amp.
Talking about the Titan in this thread has made me want to bop the amp back out for a while.

I always liked how tubey it sounded. It's a great package, though pricey. But I always felt it was a way better amp than some of the other > $1K heads I've personally tried, such as the Aguilar DB751 which was very boring sounding to my ears. More so when you consider it has barely any features in comparison, costs more than the Titan (particularly used), and there's no local service with Aguilar, you have to pay to ship things back to them (both ways if I recall). In contrast the Mesa has more features than you're likely to use, excellent support from the factory, and locally there's 2 authorized shops if I need repairs.
MESA has a lot going for it, both as a company and their products. If I had any gripes it would be the cost of their gear.
I've had an itch to buy a 400+ to see how much fun one of those are, purely just for the hell of it and not because the Titan leaves me lacking anything. But the 4U size and the all-tube aspect makes me a little nervous to be honest. Tube are expensive, and my Titan still has 4 years of warranty left as opposed to 0 on an old 400+.