Silly? Don't see it. There have been flying ships (actual sailing ships that flew) in D&D before; SJ just categorized them and added space travel rules to D&D. Yeah, there were some strange monsters, but when has that not been a part of D&D? Also some of the ships were very strange: squid-shaped ships, whale-shaped ships, or spider-shaped ships come to mind. The Spelljammer itself was a huge creature that looked like a bigger-than-colossal manta ray peopled with several factions all trying to gain control of it or escape from it. It flew around space as it wanted and had a big city on its back. D&D has always had a claim to the absurd; I remember a gun-slinging, old western-version angel (solar) in one adventure and the silliness never stops there even in "normal" D&D. Spelljamming was what driving the space ship was called and only spellcasters could drive and lost all spells in memory just trying (taking out the party's big guns for ship-to-ship combat). Siege weapons got described fully and some new ones added. So as always, silly is a part of it like silly is a part of all D&D; but silly as the descriptor for it, I think not.
