I'm upgrading from S2 so the whole LTE, redesign thing is a pretty big deal I've been missing out. While I liked my S2 what motivated me to upgrade on S5 was how little it improved over the S4, meaning that AW are starting to get so good Apple doesn't know what else to come up with.
Sure I could see an S6 with HDR display, 24hrs battery, front-facing camera, skin contact unlock, sleep tracking, better water resistance, smart bands, and remote coffee maker but I'm ok with S5 for the next 4-5 years.