I've been on a retro kick now for months, actually, but it's always been supplemented by a current (or kinda current) gen game at the same time. I love old games, the look, the feel, the fun and experimentation they forced, all are lost on most modern games.
Most recently I've been playing Sonic Colors on Wii, Castlevania Bloodlines on Genesis and Conker's Bad Fur Day on N64. Colors is fantastic old school gaming, and blew me away instantly- It might be the only Sonic I've enjoyed since SA1 back in the day on Dreamcast. The sense of speed, the branching paths, everything that made Sonic games "Sonic" are there, and with really great level design and graphics. Floored me...
So then I started playing Bloodlines around Halloween (a game I had never finished because it is HARD) and I realized how difficult old school games really are! I beat it, but man, it was 20 hours of punishment, and a lot of times from stupid bad design choices, like sh$$ty hit detection and crappy control decisions. The game, the levels, the atmosphere all oozed old school charm, but it was a stark contrast in 'new vs. old' and how far we've come, especially in the 2D genre.
Conker is funny as hell (well, for the 12 year old in me), but like so many other old 3D games has design decisions that show their age far more than the graphics or level design. FWIW, thank goodness I know someone with this cart, they're $100 and over on eBay! He showed me the mighty poo level and I was sold, that's the kind of thing that no one would ever get approved by Nintendo these days. HotD:Overkill notwithstanding.