The Bletchley Park museum is basically everything else on that site except the NMC. If you're interested in Computing then yeah the NMC is the only part worth visiting, but if you're interested in intelligence, code breaking etc. or in what life was actually like during WW2 then the museum is pretty interesting.

The house is part of the museum these days, so a ticket for the museum covers the house (which is, yes, basically just one of a great many English stately homes you might visit and not by any means the most interesting) as well as numerous huts and exhibits about the larger intelligence operation in WW2 and what else was done on that site beyond simple "breaking Enigma" (the most famous thing) and Lorenz (which is why Colossus exists)