ViperROM is a Sense-based custom ROM that does not look a lot different than your stock EVO 3D Sense 3.0 phone at first glance. It's pretty decent at not looking like there's much up. If it were a car, you'd call it a sleeper.
Under the hood you have Tiamat's Sense 1.10 kernel, which allows you to overclock to 1944mhz or underclock to 128 mhz should you be like the Comcast Slowskis (or want to conserve as much battery as is theoretically possible).
Sprint Hotspot comes unlocked for 3G tethering on the run. I don't think it's available for 4G tethering, but there's always WiFi Tether for that if you need it. The stock apps are actually removable, with plenty of bloat moved off to the side that you can reinstall if you want to. Sprint Zone has been left installed so you can dial *2 and access all the goodies it has to offer without having to reinstall it, as with many ROM offerings.
There are pages of features, tweaks, and enhancements you can view. One of the fun tweaks is the viperROM control scripts; when activated from a terminal window, they allow you to do several things, including modifying the overclocking daemon (think SetCPU), adjust the brightness of the capacitive buttons (home, menu, back, Sherlock,) and freeze, defrost, or chuck bloat, among many other things.
My first impressions of viperROM were actually not favorable, but I quickly discovered most of the initial negatives were due to me having HBOOT 1.50 on my phone, as well as having to go a different route to make things work properly followed by a series of app issues. But that's not the ROM's fault; in order, it's HTC (S-ON), Superuser, and the Android Market's fault.
If you're running HBOOT 1.50 with S-ON, make sure to follow these instructions, or else you'll be left with a leftover kernel from your last ROM. What this will mean is you'll boot up and WiFi will not work, weird things will happen eventually, and people will think you smell funny. My first attempt to flash via recovery resulted in all three of the above issues.
So, try it out, see how your battery life and performance needs are addressed, and drop a line here to let us know how you liked it. If there's a feature that really needs to be listed here let me know; there just are so many little details in this ROM it's hard to pick what to highlight. It sort of reminds me of Sprint Lovers for the EVO 4G – lot of stock, but with a lot of work that went into it.[xda-developers]