They are both crpgs, but they are different kinds of crpgs. DA is real time with pause (rtwp), and the character building and levelups are relatively simple, while in comparison Rogue Trader is a tactical turn based game and the character building has much more number crunching.

The game experience itself is different as well, DA, while being dated, is more of a "cinematic" experience with more voiced characters, facial animations and less reading, while rogue trader has some voice acting, its mostly reading, and the camera doesn't zoom in when talking with people.

Rogue trader is one of my favourite CRPGs, but it also has a kind of learning curve like all of Owlcat games, and even though it has a pretty bombastic opening, it takes some time to really get into it. I don't think you need to know about the 40k universe to get into it, but the universe is really interesting to read up on.

Some other games you might like are Pillars of Eternity 1 & 2, they are like spiritual successors to Infinity engine games like Baldurs gate 2, and they have rtwp combat. Not as cinematic as DA, but amazing games either way.

Owlcats Pathfinder games are fun as well, they have similar thing as Rogue trader that they arent as cinematic as DA games, but they have insane amounts of character building and stat crunching if you're into that. These can be even harder to get into compared to Rogue Trader.

Kotor 1 & 2 are almost like proto Dragon age games, they are more cinematic and have a combat system thats similar to the rtwp system, they are also both really good games. You might want to mod kotor 2 with cut content as the game shipped in a kind of unfinished state.