Probably to date the most experimental entry in the Monster Hunter games, Dos has a lot of strange features on offer. It's got the oldschool styled city/town hub in the premiere appearance of Dundorma - probably my fav town in the series (love the vibes).
Jumbo village is really cool as well, and Dos is also where Elder Dragons, the original trinity of Teostra, Chameleos and Kushala Daora first got to show their stuff (as well as some other, longstanding secret friends :)). I will admit I haven't gotten too far into Dos myself so I can't really speak on the quality of the Elder Dragon fights, but I will say that the "seasons" system is incredibly novel AND COOL!! It was actually a real big shame that it turned out they weren't bringing it back for Wilds since that was the kinda vibe I was getting from that game's weather system at first. Back to Dos though, the game is really neat and it's a shame that it's stuck on the PS2 with dead servers.