We've tried out the Lab Challenge (from the new In The Lab expansion), and I can't quite tell if it makes the game harder or not.
All other things equal (#players, roles, # epidemics), is a game with Lab Challenge easier or harder than one without?
As with the original game, the more you play the In the Lab expansion, the better you get at it. When I started playing the original version with my friends, it was hard to win with 4 regular epidemics but, by the time we got the expansion pack, we were beating the game easily with 6 epidemics (or 5 virulent strain epidemics with the added mutation disease if you have the On the Brink expansion). With the In the Lab expansion, we have almost never been able to win with 5 virulent strain epidemics and the mutation disease. It seems like the more you add (such as virulent strain and mutation) In the Lab is harder than the regular game, but it will all depend as time goes by.
It won't make the game easier or harder per se, but it gives more freedom for the players to move since while on the original you have to get 5 cards of the same color (what keeps leading players to meet with each other constantly in order to pass cards) when you add the In the Lab mechanics instead of meeting the player the card you otherwise would pass can now be used on the lab spots.
While this is a bit more complicated than the original mechanic it is way more thematic and let the players move more freely. I don't think it makes the game easier or harder but it does make the game better and more enjoyable, specially for experienced players due to the added complexity.
From what I've seen, it makes the game harder. With on the brink expansion, we were sometimes winning with 6 virulent epidemics and the mutation challenge but now we can't even manage to win with 6 normal epidemics w/o any other challenge. Takes more actions to find a cure for sure imo considering you have to collect a certain amount of cubes and then move them throughout the lab and sequence and characterize. Anyway, it makes the game evenmore complicated and enjoyable still. Peace and love