Ah, the delicious Dr. Reid.
There are a bazillion reasons to love Spencer. He's a certified genius with an IQ of 187, has an eidetic memory that allows him to remember ANYTHING he's ever read, and is so socially awkward he's just damn adorable.
What the series seems to point out is that Spencer makes attachments very quickly and is extremely loyal to those people. He's the youngest member of the BAU, which leads him to be treated almost like a kid brother you just feel really bad for. His almost surrogate father is Jason Gideon (played by the amazing Mandy Patinkin), who watches out for him. The two frequently play chess together and seem to know what the other is thinking. When Gideon leaves, it's Spencer who figures out what's going on, and though he tries to hide it, he's crushed. After that, we get a more hardened Spencer, though he still attaches himself to new agents, Emily Prentiss in particular.
Speaking of cuddling, here he is with a puppy:
|*Dies of Squee*|
And a couple more gratuitous Spencer photos.