lori123 - In the case of the OP of this thread (VandVsmama), I thought that June might be a better choice. But personally I'm a big advocate of going during the Halloween Time season and enjoying the various treats, decorations, the Halloween party, the ride overlays, etc. So if you are a Halloween fan, then most likely you will enjoy Halloween Time at DLR. If you want to find a time to go to DLR when it won't be crowded, I don't think early October is a good bet.
October - especially the first couple of weeks of October and that last week leading up to Halloween - is very busy. Not New Year's Eve busy. Not scary busy. Probably not 'filled-to-capacity' busy. But there are very long lines for rides and there are pretty big crowds. It's not the same ol' off-peak season that it used to be. I could detect a definite, palpable increase in crowds just between 2008 and 2009. Some folks said that the 2010 Halloween season was the busiest one so far.
When DLR starts to add new attractions and events, more people show up to see them. This year will see 2 new rides opening (well, Star Tours will pretty much be new).
You can still have a great time even if it is really crowded. Also, I am finding more and more that people perceive crowds differently - what one group says is way too crowded for them, another group will say is completely tolerable and manageable. So if you have your heart set on October, you should give it a try!