WiF increased the defense value of land units by a large scale this makes the firepower overload unlikely in WiF unless the force ratio is very very large between attacker and defender. This has the result making battle longer and which in turn lead to more losses.
With the longer battle time, AI often has plenty time to reinforce the spot that is being attacked. This makes traditional breakthrough battle much harder for people who are only used to vanilla game. You of course also get more time to reinforcement the weak point in the line just like AI does when attacked.
It does take more planning for WiF when attacking, which makes the game more interesting. The events are better as well and with more flavour.
I personally don't particularly like the tech tree set up, but that is just me. Also the terran map color annoys the hell out of me in it, I like the vanilla better.
Overall speaking it is a good Mod, best experience by playing Germany or Soviet Union, some very fun events for the first players.
Make no mistake AI will get some help like free divisions for Soviet Union in events, some may say it is cheating, but honestly AI need all the help it can get.