I have played all of the Heroes of Might and Magic games and I love them all. They have the perfect recipe for strategy games and they continually tweak them with each iteration and have only gotten better (5 is amazing). However, HoMM2 holds a special place in my heart as my favorite of the series. First, it was the first game in the series I was introduced to and was my first turn-based strategy love. Second, I think I enjoy it most because it has more complexity than the first game yet not as much as later titles. I felt something was lost by adding too many new things to the game and I enjoyed the simplicity of the second one. I also like the graphics for their simplicity, they are beautiful and very expressive but don't try for more realism like later games in the series did. I think something was lost in that artistic process and those games look more drab for it (except for 5 which went to a more cartoonish look which brought back the colors and such). I highly recommend this entry in the series to anyone who is a fan of turn-based strategy games.
