I'm not impressed but I don't really dislike it either. It's easy to see these as they are 10 minute drive from the airport. Use one of the ride apps to get a car to drop you off easily. Echmiatsin is the easiest because it's the town of Vagharshapat itself, with a hotel directly across the traffic circle if you want a convenient place to stay (Richmind, cheap and comfy). Unfortunately as you can see from my picture it was closed for renovation.

While the infrastructure is not bad in any way, the Armenian style churches are not special enough in this area. So I think it was more inscribed due to "imported" structure knowledge at the time to show culture moving around the world/regions - I don't find that fancy enough for a world heritage. Because it's an easy visit (oh no she said "easy" again?!) I would recommend throwing it on your itinerary even for non-WHS enthusiasts.

Zvartnots is best done on the way to/from Yerevan and it won't take you long to see everything either (I didn't say "easy"!), it's got ancient ruins from the old buildings and a better view because there is no town surrounding the site. So once again, don't expect to spend much time here and don't have high hopes of seeing something fantastic either.