If you want to judge it on just being a transport... Ok, yes its more expensive than just about any other transport. But for that cost it can go further than just about anything, get a 3+ cover save when going flat out, and thanks to the serpent shield you don't really even need to worry about the explosion result wrecking half the unit. Also, a transport is only as important as its cargo and the Serpent can carry some of the scariest things out there.
As a fighting tank, it rules the mid-strength shots field, is pretty darn durable with its plethora of rules, and is mobile enough to be a threat from many facings. Comparing the firepower to other transports is really an unfair game as most have either a single strong shot or a couple weak ones. Only the Night Scythe really stands up to it thanks to being a flyer.