I generally don't buy DLC because I'm not interested in things like extra cars, costumes that don't really add much to the gameplay. It seems silly to buy more cars when the base game already comes with 50-100 cars. What I value are things like extra tracks and new areas to explore, but for developers, its just way easier for them to do things like costumes because people pay for shit like that.
The best DLC/season pass stuff so far has been -
1. Dark Souls/Bloodborne - brand new areas which are more expansion packs than DLC. Definitely worth the price.
2. Mario Kart 8 - probably the best priced DLC ever and giving people tracks, not cars.
3. The Witcher 3 - haven't played it yet, but Hearts of Stone and Blood and Wine looks to add 30+ hours. That's more game than most other base games. I'm still waiting for a sale.
4. Driveclub - Even though this one is just tour packs for the season pass, I'm still keen on getting it because I really enjoyed the season mode in the original Driveclub. I need to catch it on sale one of these days.
The biggest offenders are -
1. Battlefield series - while the content is pretty good, lots of maps. it's priced the same as the base game. It's like paying twice the price.
2. Anything with a deluxe edition for $10-20 extra over the standard edition that sells you costumes, coins, skins, weapons and really trivial stuff that should already be included in the game. I guess I'm fine with them releasing that so people that want to pay more can, but I can't see myself buying it.