Edit: This thread was started to show a tempest build that works for a semi-casual player. Good enough to solo R2-R3, and contribute in groups in R4-R8.
So my main has always been a Dex-based TWF evasion character. Almost always with at least 6 levels of ranger.
Since reaper came out, I've been messing around with various build ideas that will allow me to solo at least reaper 3, but also be able to contribute to high reaper PUGs.
Max ranger DPS (aka Tempest 20 running LD) is best if you have a good guild or a static group with lots of CC and/or healing and/or tanks. But a max DPS Tempest is somewhat of a glass cannon when soloing. It's easy to get overwhelmed by a group of mobs on reaper, and your self-heals aren't enough to keep up with the incoming damage.
So I kept experimenting with different trade-offs to give myself more defense and survivability, but not nerf the DPS output too much.
Multi-classing means you lose the Tempest capstone, and maybe even the level 18 core
First thing I tried for fun was adding some warlock levels. I played a 14/6 ranger/warlock for good amount of time. The warlock aura ticking off 150 temp hp or so every 4 seconds was hugely useful in low reaper. I also really liked Dark Delirium... a no-save single-target Daze Monster that lasted for 30+ seconds. It was a great way to shut down a dangerous champ or a reaper.
But the MAIN advantage from the warlock levels was access to quickened Sleet Storm. This spell slows down enemies 50%, and gives you sneak attacks on them (I run with Scion of the Ethereal Plane, which is all about sneak attack damage). I found this hugely useful when soloing large packs of mobs (14 ranger can self-cast FoM so Sleet Storm doesn't affect you).
But warlock levels aren't nearly as useful in high reaper PUGs. The 150 temp hp every 4 seconds just isn't enough to matter, and in groups it's harder to get people to use Sleet Storm. It COULD work with a tight group - you just have to make sure to cast FoM on everybody, and choose choke points together, but most PUGs are fast moving, and less likely to use enough teamwork for Sleet Storm to be useful.
So although warlock levels did help with soloing low reaper, it wasn't very useful in high reaper PUGs.
And then the Epic Defensive Fighting feat came out, which doesn't work with warlock Aura, so that made the warlock levels even less useful.
One of my alts is a barbarian, and I really like Blood Tribute in reaper. It's very very good in low-to-mid levels heroics (150 temp hp), and pretty good at epic cap as well. 400 temp hp that you can spam every 3 seconds at cap does really help in a big fight, even in the higher level reapers.
I thought maybe I could incorporate 2 levels of barbarian into my ranger character.
For fun, I tried a 14/4/2 ranger/warlock/barb character. The warlock levels were ONLY for Sleet Storm, no aura, not a single AP spent in warlock enhancements. I got blood tribute from barbarian, which was (mostly) better than the warlock aura, plus I could use Epic Defensive fighting for more base hp.
That build was successful as well. Just as good or even better soloing low reaper, and still decent in high reaper... but again, I wasn't using Sleet Storm in high reaper groups (so the warlock levels were wasted).
So, for a while, I took Sleet Storm off my hotbar, and tried soloing without it. If I could solo without it, I could move up to a 18/2 ranger/barb build, and get a bit more DPS from that level 18 tempest core. In LD, soloing was fairly solid, but there would still be times I would overwhelmed.
So then I added another twist. I switched to ShadowDancer ED, instead of LD... That seemed to do the trick when soloing... 25% incorporeal from Shadow Form adds a lot of defense (30% with the level 18 tempest core). Meld into Darkness is huge, 100% dodge for 15 seconds has saved my life many times. It's hard to calculate the DPS loss at cap using SD instead of LD... You get a lot of sneak attack bonuses in SD. Standing melee power is easier to deal with than Blitz. There are times when I mess up (or the group is too slow), and I lose Blitz. I have 42 more standing MP in SD than LD. When Blitz is fully active, I have 28 more MP in LD. But with the extra sneak attack in SD, I think DPS from Blitz melee power is a wash.
The real difference in LD is Combat Brute (and 20 second cooldowns on Haste Boost). 50% more damage on helpless enemies is huge. But note that only applies to trash and not to bosses. Boss DPS is just as high or higher with ShadowDancer.
So far, I've been pretty happy with SD. I can solo low reaper with very little chance of dying, contribute well in high reaper, and I'm durable enough to survive in high reaper even when on my own for a bit. I certainly can't solo high reaper, but I can take down a pack of mobs on my own if needed, and with CC or a tank, of course, I do a ton of damage.