Its still a good chip, especially with an easy OC to 4.2 - 4.4. I'm still running mine and have contemplated upgrading but can't justify the cost really.
I run VMWare workstation with 3-5 VMs at any given time, and GNS3 (routing lab software), all which use CPU cycles and a good amount of RAM and this thing still handles it just fine. The only thing that may force me to jump is my current limitation of 32GB or RAM.
The big drawback with Z77 and the 3770K is (native) 16 lanes of PCIe 3.0. To thwart this you can get a board like the EVGA Z77 FTW (which I did) which has a PLX chip and gives you four slots at x8 each. Now I've got a GTX 970, an LSI 9266-8i RAID card, an Intel dual-port PCIe gig LAN card, and another open slot for whatever I may want (could SLI a 2nd card if desired).
The 6700K and Z170 does bring a lot of new features, a real-life 30% boost in CPU performance (at stock speeds) and a higher ceiling for overclocking. M.2 interfaces for PCIe SSDs, tons of SATA, more PCIe lanes from the chipset (instead of the CPU), DDR4 memory support, 64GB RAM support, and a much faster bus speed (though it would take a LOT to even saturate DMI 2.0 on all other consumer chipsets). You're looking around $600-$1000 to make that jump though, depending on what mobo and memory you choose.
Note that the jump to X99 and 6-core 5820K can actually be cheaper, and is something to consider if you really want a strong jump in CPU performance (if more than 4 cores will actually benefit you). If you're high on overclocking you want the 6700K on Z170 though as its designed for it.
I happen to have an ASRock Extreme4 mobo for sale if you think it will give you a couple features you think might get you by. Just want to get rid of it really.