I didn't play the heroes games in a row too!
I started with H3 and after I had finished all campaigns and played let's say a lot(
) I wondered what the backstory of H2 was. It took some time to track it down as it was already rare and found out that although not as good as H3 it was more addictive and fun!
Then after a strange streak of coincidences a friend of mine running the dos found out that the H2 cd also had H1 hidden inside
Didn't play it a lot as it was nowhere as appealing as H2 though it was quite different.
Then H4 was on the horizon and I was overjoyed! It lasted for a while but I was disappointed about some things that didn't allow me to enjoy it as the previous ones. Still a good game in its own right.
And of course the unexpected H5 which I still enjoy but I'm disappointed in that it could have toppled H3 but failed for several reasons. So much potential that could make it from good to exceptional...The support only makes things worse.
My suggestion: After you've played H5, try H3 and then H2 or H4. Try not to mix them all at the same time. All games were good but you can only spend so much time on them! If you have friends to play together you will enjoy it so much more!