1. Ghost in the Shell
My love of this series probably has something to do with the fact that Blade Runner is my favorite film. This show has everything ... endearing characters, philosophical pondering which (usually) does not get excessive enough to bog down the plot, fascinating story arcs and villains, and a healthy dose of cyberpunk action.
2. Ergo Proxy
One of those weird weird shows that I had to watch at least twice before I could say with confidence that I understood the whole plot and all of the little details. A great show, but one that I rarely see anime fans talk about even if they have heard of it.
3. Serial Experiments Lain
Got a thing for the weird stuff, and the sci-fi / philosophical overtones make this one memorable too. Lacks a plot as deep and unique as Ergo Proxy and Ghost, and is not nearly as re-watchable as them.
4. Texhnolyze
Like most of my list this is sci-fi and obscure. Took me a good 5 episodes to warm up to it, and I will be the first to admit it is slow, but I still appreciate it for just how unique it is. It is one of those series I would watch maybe once in a great while ... may skip some of the earlier episodes next time I do.
5. Gantz
This is the only series on my top 5 that I don't own, but I would probably pick it up if I ever found it cheap. A fun gore/sci-fi extravaganza that pulls no punches. Unfortunately, it has one of the worst forced anime endings I have ever seen in a series. I understand that an anime can usually only go on for so long, but the ending was just pathetic leaving absolutely nothing resolved. The writers just tried to (in the span of a few episodes) attempt to supply some kind of message to a story where it was completely uncalled for (just like in Evangelion, actually). Gantz still makes my list though for all of the episodes being a fun guilty pleasure of sorts up until the last few. My advice would be to watch the series up until the end of the third "game" and then just stop and make up your own ending (which will probably be much better than the actual ending). Either that or go read the manga which continues the story.
Honorable mention: Cowboy Bebop. This is the second mainstream series I enjoy, but it doesn't make the list for lack of any substantial and meaningful plot, or even the raw hedonism that Gantz provides. It is a great series overall, but too many episodes are filler/ are interchangeable, and the main plot between Spike and Viscious takes way too long to get going. It seems uncessary too. One gets the impression via flashbacks / ect. that there is a lot more history between these two characters than the series will show, but we never get the chance to explore it. I would definately watch the series again though, but I think I will have to skip any and all episodes with Ed taking up extensive screen prescence since she has to be one of the most annoying characters I have ever seen in an anime (and I have seen at least 50 different series by now). I must also say that Bebop has one of the best endings to an anime I have ever seen (this is not saying much since anime endings tend to suck, but it is still worthy of mention).
