I enjoyed Battle Missions, it was very useful actually. I didn't play much of Spearhead (only one game), but it seemed ok in an Apocalypse-Lite kind of way. Planetstrike was good, but some of the requirements and special rules (more terrain) meant that playing it involved transporting a tonne more stuff.
Since the rules update we have also had the Crusade of Fire and Death from the Skies supplements. Honestly, I think GW are producing a lot of stuff these days. Their codex releases have certainly been coming much faster. As for changing the rules so often, an update every 4-5 years doesn't seem unreasonable. I had no problems with 5th, but 6th is fun and different enough that I can enjoy that as well.
More on topic, whilst I wont be buying an Eldar army, I am certainly looking forward to seeing what cool new toys they get once they are updated. Then, when I play M_i_J, I can feel happy that I lost because his codex was new and cheesey as opposed to losing to an older codex and feeling miserable about being a terrible player.

Painted Minis in 2014: 510, in 2015: 300, in 2016 :369, in 2019: 417, in 2020: 450