We didn't feel crowded at all on Oasis until the last day -- disembarkation -- which was a mess. In fact, there are so many quiet spots on the ship. We especially enjoyed listening to the classical music performance by the pianist and violinist in Central Park every evening! Hardly anybody were there.
We watched every show including the comedian. Most shows were not fully attended (apparently a lot of passengers who made the reservation didn't show up). There was no problem to get in even if we were on standby on some shows. The two and half hour full version Broadway Show "Cats" is phenomenal. It is even better than the one I watched in NYC!
We did most things on the ship, i.e. rock climbing, surfriding, ziplining, ice skating, jogging.....and even cupcake making. The lines were short especially on port days. We have dined in most restaurants, i.e. free and for fee. The only disappointments were Johnny Rocket and the MDR. The duck and lobster on formal night in MDR were way overcooked. Chops Grille is outstanding. MY only complaint about Oasis is there is no library (I really enjoyed the spacious library on Holland America). But judged by the jam-packed casino, apparently RCCL caters to a different clientele.
Spacious but noisy whenever the ship anchors at harbor.