FWIW, my experience with the Alienware x51 (and I may get pummeled for this, but it’s my experience as a PC gamer that started in the spring of 2012):
I initially bought an x51 for the same reasons as you cited, i.e., didn’t know much about PC gaming, wasn’t too confident in building myself, wanted to start gaming right off, etc.. I started with the following:
i7-2600 Intel processor
8 GB Ram
GTX 555 OEM 1.5 GB
For the time, it was a mid to high-end gaming pc...