Even by today’s standards for a 2014 device, the stock ROM is remarkably smooth. HTC optimized Sense aggressively. Animations are buttery (60fps in the UI), app switching is snappy, and there is very little "touch latency." It outperformed Samsung’s TouchWiz of the same year by a wide margin.
The stock ROM included native support for HTC’s iconic Dot View case. Without any extra app, flipping the case closed would show retro pixel-art animations for weather, calls, and battery. It was a brilliant piece of hardware-software synergy.
If you run the final official stock ROM (Android 6.0, 2015-2016 security patches), it is dangerous for daily use in 2025. There are dozens of known vulnerabilities (Stagefright, BlueBorne, KRACK) that will never be patched. No modern banking app or password manager should trust this environment.