T 20 is designed to be a Batsmen's game. Every single rule favours the Batsmen. Bowler has to always bowl in the hitting zone of the Batsman, he cant bowl bouncers at will, Boundaries are ridiculously short, there are normally no close in fielders to snaffle up the edges, no restrictions on the bat means even mishits get hit for sixes..... the list is endless.
On the pro side, Batsmen are trained now to look for runs, which has had a positive influence on Test Cricket, and even ODIs. They score at a much faster pace in Test Cricket, making the matches more exciting. I remember once in 1981, travelling for 2 days in Train from Palghat to Delhi to watch India play England at Feroz Shah Kotla in a Test Match. England won the toss, and Boycott and Tavare batted the whole day and England ended up with 186 for 1!. Those days are gone.
The Batsmen are very innovative, and aggressive. Improvisations galore. Reverse Sweep, Steering late to third man, scoop over wicket keepers head and the ability of batsmen to find the gaps are definite advantages. The running between the wickets have improved and it is a pleasure to watch athletic batsmen like Virat Kohli, A B Devilliers etc run like hares between wickets, converting ones to twos. A couple of days ago, David Warner and Bairstow ran RCB ragged with fantastic running between the wickets.
Batsmen are not afraid to loft the ball, a far cry from the old school of batting. I remember having to run two laps as a punishment for lofting the ball while batting in the nets in 1980s. The Coach was furious, as we were taught only to drive the ball along the ground.
On the con side, sound technique, especially defensive techniques have totally disappeared. In Test Cricket more batsmen get out nibbling the ball outside the off stump, a carry over from their T 20 matches, where they can get away with it. Today's Test Teams cant play out 3 sessions on the final day to save a Test Match, though there are have been one or two exceptions.
Batsmen are losing the ability to play the short ball. T 20 expects them to plonk the left foot forward and towards mid wicket to hoick an ugly cross batted swipe. This creates a major issue when the ball is bowled short, and we see more batsmen getting hit. With the batsmen getting to play in flat surfaces in T 20 all the time, they are found wanting when the pitch offers something for either the fast bowlers or turns for the slow bowlers. There is a marked deterioration in the skill sets of the batsmen overall. Loose technique, coupled with over arching aggression, enhanced risk taking have led to shorter stays at the crease across the formats. Once, not long ago, good Batsmen used to put a price on their wicket. Not any more. It almost appears Batsmen dont mind getting out, as it happens frequently in T 20s.
Saddest part is that Batsmen feel an entitled lot, having all the rules framed in their favour.