As a Gally grad, I may be somewhat biased.
Gally has an ASL program during the summertime for new students to undertake if they do not possess the requisite knowledge of ASL. Granted, this 2-3 week program is still inadequate and most new students will get lost initially in his/her first semester at Gally. However, the vast majority of such new students should eventually get better and become adequately proficient by the year's end.
As for your question about the general quality of education, it really depends on what line of study you are contemplating at Gallaudet? If it's Deafness-related, you've come to the right place. If not, then Gally is just like any other liberal arts university with strengths and weaknesses.
Overall, the undergraduate student body's educational acumen is lower than student populations across comparable universities. Thankfully, the university's graduate student body more than makes up for the shortfall.
If you are feeling a little bit adventurous (sp?), you can contact the university and arrange for a personal meeting with a recruiter or an alumni representative. This should help alleviate your concerns about acquiring ASL in midst of your studies and the quality of the university's academic offerings.