I've completed 1500 raids in D1 and over 1000 raids in D2. 99% of those raid completions were through LFG, and I've only had a handful of bad experiences. At first, the raids might take a little while if you and/or others are unfamiliar with the raid and encounters, but as you get more experienced, you can request more experience from other players and fthe raids go much faster. Every currently available raid can be completed in less than an hour.