It will be nice going to a 120Hz monitor if you do a lot of gaming - since the 120Hz refresh rate will make fast motion feel smoother, the response time is lower (so less ghosting) and the input lag is a bit lower.
However, in terms of picture quality - your Dell will look nicer than the Samsung because your dell uses a rather nice S-PVA type LCD panel, while the Samsung uses a TN film type panel. S-PVA has the benefit of rather high static contrast ratio, good black level, pretty accurate colours and relatively wide viewing angles. While a TN panel doesn't have as good static contrast ratio, black level, colour accuracy or viewing angles. Also, the Dell uses a 1920x1200 resolution (16:10 aspect ratio) and the samsung is 1920x1080 (16:9 aspect ratio) - so the dell does have a bit more vertical resolution, so more screen real-estate, as well as slightly more viewable area due to the less wide aspect ratio and the same diagonal size.
As I say, the Samsung will be a better option for gaming and 120Hz 2D will look great (plus 3D gaming is possible) but don't expect the image quality to be any better than qhat you currently have.
If you would like superior image quality then I would have a look at a 27in 2560x1440 IPS panel monitor. These have superior image quality both due to a generally better panel technology and a higher pixel density.
