Depends on the frailty of the escort, and the design of the stealth. Some Escort Missions are more like you are being escorted by someone badass.. Those are pretty sweet. Even if the goal is "Don't let this person die", if they're badass in their own right, or interesting to listen to/watch, then yeah, I'll enjoy the mission. Likewise, stealth can be either good or bad too. Some games do it really well (I'm going to say Windwaker, but I KNOW that it's the posterboy for useless forced stealth sequences, but I liked it), others it just feels stupid and worse off, it's difficult.
I'd say Escort though. There's only been one game I can think of (Ico) that stretched an Escort Mission into an entire game, but many games have been successful at stealth.
I just really hate having to protect someone else in a video game when my own actions are sometimes difficult enough.
That's what it really comes down to - how difficult is the mission.. if it's really really hard, and it's a gimmicky mission, like a stealth or escort, you'll blame the gimmick. If it's easy, or fun in general (Liberty Prime), then yeah, It's not bad.
In general though, Escorts tend to be worse due to the frail nature of the person you escort.
