You'd better be on time.
Remember: Check-in for every flight closes 30 minutes prior to scheduled departure. It's hard for some to accept that they have "missed" a plane that in some cases hasn't even arrived at the gate, but that's the easyJet policy. As we've noted, they generally don't make exceptions unless extenuating circumstances exist for a number of passengers. You've been warned. You'll be warned on your confirmation email, too. And you'll be warned by big signs in many of the airports. Plan accordingly.
Heavy baggage will cost you.
Each passenger's total luggage weight allowance is 50 kg. (110 lbs.), with no single bag heavier than 32 kg. (71 lbs.) But those with baggage weighing in excess of 20 kg. (44 lbs.) can expect to pay an additional fee, and there is also a fee structure for larger sporting equipment such as skis or golf clubs. The fee for excessive weight is £5 or 7.50 for each kilogram.
The early-bird (usually) gets first choice of seating
With no assigned seats, it's first-come, first-served on easyJet. There are generally four boarding groups, identified as A, B, C and D. These are filled chronologically by time of check-in, but we made it into group "A" twice only because children were in our party. Agents on our trips clearly put people who need some extra time or assistance in the "A" group.
Final thought: my easyJet experience was good.
Budget travelers do not mind being pampered, but most realize saving money often requires sacrifice. On easyJet, I found those sacrifices are minimal. I saw no difference in seat comfort or service. I travel without heavy baggage, so there were no weight fees to pay. My savings on airfares more than compensated for the higher ground transportation costs.
Your experience with easyJet or any other budget carrier could be far different. But the benefits on my flights far outweighed any drawbacks.

