TOAW III, and AGW, along with Advanced Tactics Gold are my main alternatives. TOAW comes with so many scenarios so that even if only a tenth of them suite me, I'll still have a lot to do. AGW also comes with quite a big range of scenarios. Still, DC is tempting, and what you say matches what I've heard elsewhere.
I already have (and enjoy) Unity of Command, but was looking for something moderately more complex and bigger... but without going into many hundreds of hours campaigns territory. The UoC scenarios I've played so far take about an hour or two to get through... I'd be comfortable with scenarios taking 4-6 hours. But 30+ (or 100+) hours is too much for me!
I like the looks of the card system - coming from a boardgame background, there have been lots of experimentation in boardgames about bringing both historicity and interesting decisions into games without overburdening them with complexity - if some of those ideas can spread to computer wargames, I think that will bode will for the future.
As for another game with Sea Lion... I've got HPS' The First Blitzkrieg, which includes Poland, France and Sea Lion... but much less appealing interface than DC, as well as too big scenarios (not all of them, but a lot of them are huge).
As far as DC: Case Blue, I just read this in a preview:
"over 150 Generals each having their own stats and biographies.
[This] is a much bigger, longer game lasting one year with two days per turn, with 700 to 800 units per side, each hex representing 10 kilometers with maps that can be as large as 160 by 125 hexes, as in the case of the campaign scenario map spanning from Kiev to Baku."
Yuck! Yes, I am overwhelmed. 180+ turns, enormous maps, way too high unit counts... no matter how much I enjoy the game's systems, I doubt I'd be able to enjoy such monster scenarios.