Performance
Low profile, sloped armor, speed and high damage make this tank very useful in all situations, particularly in urban and close-range combat. At this tier the once-fearsome 122 mm D-25T bounces off enemy armor more frequently, so try to get side shots when you can until you can research the BL-9. The upgraded BL-9 gun wreaks havoc on tier 9 tanks and below, although it won't always pen the front of other heavily armored tier 8 tanks. The Gun Laying Drive and Vertical Stabilizer are reasonably effective, but taking more than the occasional potshot beyond 300m is not recommended. Angled properly, the IS-3's armor will consistently bounce shots from other tier 8's and below, especially from the front. It requires no frontal angling because of its frontward-angled "pike" front plate; counter-intuitively, trying to angle it further will ruin it. Instead, point the tank straight at the enemy & close the range to hide and/or increase the angle of your lower glacis. Be careful about closing inside 50m, as the center turret roof panel is extremely prone to overmatch, especially at very close range against taller tanks, of which there are many.
Its playing style is well-suited to aggressive force leading and peek-a-booing. The IS-3 will find itself at home on urban maps and other maps that allow it to take cover and move to get close to its target. A semi-hull-down position works well in the midrange, covering the vulnerable lower glacis and forcing shots to be taken on the effective frontal armor or extremely hard-to-penetrate turret. Thanks to its spaced side armor, it often takes non-damaging shots on the sides, but the tracks tend to get damaged often. Once the 122 mm BL-9 is unlocked, the IS-3 displays truly fearsome power and is among the kings of tier 8 tanks, able to threaten even tier 10's.
Contrary to popular belief, the little hole on the front of the the turret is not a weak-spot, the tracks are very good at eating shots, and the sides and corners have spaced armor, thus making them areas where you will shoot but almost certainly do no damage whatsoever.
Early Research
The V-2-54IS engine, the 12RT radio, and the 122 mm D-25T gun carry over from the IS and can be installed immediately, putting the IS-3 in a great starting position.
Start by researching the upgraded turret. The extra meters of view range, additional 50 hit points and greatly increased armor and sloping can make a difference.
Researching the fearsome BL-9 next will boost firepower, turning this tank from an opportunist to a grade A brawler.
For an additional 3 deg/s traverse speed, one can research the upgraded suspension before the top gun, but the added weight capacity isn't necessary.