The Ducs is a rock-solid, high quality traditional 4* hotel. We all have our own standards (I 'think' mine are quite high) but: service was excellent, flexible, generous, interested, reliable, personal, homely. The discount to Megeve is spot-on, especially drinks; the quality of food and drink is high, higher than expected, with buffet spreads (a constant source of whinging for me) absolutely irreproachable. Rooms are cosy, clean, tidy, traditional, and 'mountain side' views are stunning. Combloux is quite - so if you're looking for clubbing expect to pay €60+ for your round-trip into Megeve, but if a bar or two, 3-4 decent enough local restaurants are fine with, crucially, easy access to Megeve (village bus to main bus stop, in your skis, then resort-to-resort navette to Megeve) takes 20-40mins depending on your timeliness/connections. While in Combloux, use http://www.locaskouil.com in Combloux - once you've met Fred you'll know why - extraordinarily friendly service.
Re spa, we didn't use the facilities that much, but they looked fairly small/limited (not a reflection on quality), so can't really comment. But once you're sat in the never-too-busy, wood-fire in the corner, lounge with a glass of wine, relaxing after a day out, you'll feel pretty good about having stayed here, even without massive indoor pools etc etc.