The 737NG has (IMO) a noticeably 'harder' suspension than older models up to the -500, making landings feel heavier. The longer fuselage also causes slightly more concern about tailscrapes and perhaps subconsciously limits the flare before touchdown some pilots apply. I've flown older-model 737 for 12 years with 3 years on NGs (700s, shorter than 800s).