the dt770 are closed
the dt880 are semi-open (please consider them fully open though)
the dt990 are fully open.
not sure if the drivers are all the same between models or related (i've heard both). they do share the same characteristics though.
dt770 are going to be more bassy with just a bit less treble than the 990. the 80ohm is most bass. the 250ohm is most quality.
dt880 are going to be a bit more neutral with a bit more subdued bass and treble.
dt990 are going to be a bit bright on treble with more low bass than 880 but less than 770. they do have more mid bass then the others.
curve graph 880-990-770 to give an example of strength of bass/mid/treble between the lines.
here is a graph comparing it to the 598, q701 and hd600
soundstaging will be biggest on the 990 and 880 and smaller on the 770 due to being open vs closed. however, for a closed headphone the dt770 soundstage is on the larger side. other headphones like the AT ad-xxx series will have larger soundstages than beyer cans though the beyers are fine for gaming if you like how they sound.
good source to check out
http
/www.headphone.com/pages/build-a-graph for response curve graphs of different headphones.
from the response curve graphs you can infer about what they will sound like in terms of quantity. for example a headphone with a mostly flat curve will be considered flat. a headphone with sharp peaks will have more noticible (example bass, mids or treble) compared with the rest of the spectrum which is not so peaked. a more shallow curve is less aggressive and blends in a bit more instead of on less frequencies.
please remember you can not infer QUALITY from graphs. things such as how detailed headphones are, soundstaging, positional audio, dark/light or warm/cold are all things best heard from personal opinions (though they may of course differ from yours) or by listening to them yourself (ideal but not always possible).
beyers are great for people who like more than average bass response paired up with bright detailed treble. they all will sound a bit recessed in mids though the 880 is a bit more flat.
i mentioned a few alternatives earlier although i know in uk many of the choices are quite a bit more expensive than the beyers. of course the cans i listed arent the be-all-end-all of lists you can pick from just ones i am fairly confident recommending and comparing against one another sonically. head-fi is a great place to read some reviews on different cans or try to find less well known choices that may be also a good price in your market (country).