It's a sampler so can be used for whatever music style you want. Although primarily sold as a drum machine due to it's heritage at the end of the day like others have said, it's as close to an Octatrack as you can get in software, in fact they've only just added probability to the OT (thanks Elektron!). The OT has 8 engines the same as Geist, Geist has lanes instead of P-Locking, so there is a different creative method involved but essentially similar capabilities. Nobody would call an Octatrack a drum machine, although it can make a very good one, I actually owned a 2nd one I used just for that purpose for a couple of years. So comparing it to a Drum Machine is a bit irrelevant imo as it's just one of the many things it can do (and do well). It's a sampler with powerful Sequencers and it is a real sampler in that it samples too.
Geist goes a lot further than the OT in terms of the amount of samples you can use due to layering and 64 tracks per engine, on the OT you can have 256 samples in a project and you can use p-locking to access 128 of theme depending on your machine type. It's definitely easier to access them in Geist although p-locking is a method that is fun and yields unintended surprises. But I think that Geist has that exploration type creativity with it's real-time pattern changing, which has the fun and surprise aspect, but you need to set up a few patterns in advance to switch between and a tip is to leave one blank as an off state to switch to (if you are running it in sync mode).
In terms of Geists' complexity, it can be overwhelming at first I guess, but like the Octatrack you don't have to use it all but it's there if needed and as you become more familiar with it. Geist can be used in a very simple way.
I'm rambling a bit (and I've just got up) but my point really was that if you've ever lusted after an Octatrack then this is the same ballpark even though they diverge in their own directions in certain ways. That isn't to say it is an Octatrack replacement because the Octatrack experience is an important part of the whole thing, especially using the sequencer. I think that is also true the other way around though as Geist can do many things that the OT cannot especially in the FX and Modulation department and the pattern switching that I keep banging on about