Of course, as with most slice of life, there is VERY little in regards to a plotline in Minami-ke. Most of the episodes could probably be watched separately as stand alone comedies. The only "plots" that exist in the series is the story of Fujioka's affection for Kana, Makoto's and Touma's crossdressing, maybe a few other minor details that aren't coming to mind right now.
The characters and voice acting is what really gets me about Minami-ke. The characters are very lively, with their unique personalities, but aren't unrealistic in the way they behave. The artistic depiction of the characters is also more realistic than many other series ( not as many huge breasts flinging everywhere, or huge shapely hips, or unrealistic hair color, or girls that look underdeveloped/overdeveloped for their age). I think this "realism" is generally why I prefer Minami-ke to Lucky Star. Minami-ke still has a very high kawaii factor.
Overall, the series is funny, soft, not over-the-top, with great art/voice acting, and doesn't needlessly bombard you with pop-culture references ( if you enjoy these, I'd suggest Lucky Star).
