Druaga no Tou: The Aegis of Uruk, Sword Art Online Recommendations
The original base goal of the anime are both the same, to reach the top of the tower. However, SAO setting is a fantasy based virtual game, while Druaga is a fantasy setting based on a game.
Though it may be spoiler-ish, the second half of SAO and the second season of Druaga are also the same, to find/save someone.
There are also minor scenes that may remind you of the other anime like the boss being CG'd or even the tentacle scenes... lol...
Both about fighting with digital monsters and passing next level.
Both involve the main characters having to climb 100 floors to reach the top to defeat the final boss, though SAO is an RPG game and Tower of Druaga isn't, the characters still die for keeps
Giant tower with many floors to clear, typical RPG-elements evident in both (shop keepers, parties, hunting for rare items, trying to get stronger / level up, so on forth). No real "clear" main villain / baddie / antagonist, being focused on the towers and it's many floors, as well as the denizens that inhabits them (might or might not hold true when the story progresses... in both of the series).
Personally, I love the atmosphere of both, giving a very RPG-feel that's quite unique in this industry.
Climbing up levels, groups fighting bosses. They both have a similar feeling as people die they can't come back.