Just watch all 4 endings on youtube. About 40 mins total. Better than downloading 1.85GB and then only seeing one of the endings per playthrough.
I played through ME1, ME2, ME3 in the last month. Did every quest and sidequest possible with full paragon choices. Probably around 200 hours total. The decisions in ME1 and ME2 makes a significant difference to the gameplay in ME3. Characters you saved and did quests for pop up randomly in ME3 in almost every mission, granting you help and/or new items with unique dialogue.
The ending doesn't depend on the previous games much at all though. Nonetheless, the gameplay was great. I can finally put the ME series to bed.