The Canon EF 75-300mm f/4-5.6 IS USM Lens is Canon's first Image Stabilized lens.
Image Stabilization (IS) is a great feature. On the Canon EF 75-300mm f/4-5.6 IS USM Lens, IS lets you handhold two f-stops faster than without this feature. It costs a lot of money to buy a lens with a 2-stop faster aperture. Of course, IS is not everything - and cannot create background blur or stop action like a faster lens. Keep in mind that the version of IS on this lens needs to be turned off when tripod-mounted. Not doing so may cause the image stabilizer to act erratically.
Build quality of the Canon EF 75-300mm f/4-5.6 IS USM Lens is OK but not excellent. This is a medium weight lens. The zoom and focus rings are not smooth. It does feel more solid than the Canon EF 75-300mm III USM Lens but is also larger and heavier.
Image quality from the Canon EF 75-300mm f/4-5.6 IS USM Lens is mediocre and very similar to the Canon EF 75-300mm III USM Lens. The IS version had slightly more corner softness.
Like the Canon EF 75-300mm III USM Lens, the 75-300 IS is soft wide open at all focal lengths. Sharpness decreases as it zooms from 70mm to 300mm. However, the corners are softest at 70 and getting better by 300.
Corner and center softness decrease as the 75-300 IS is stopped down.
Stopping down a relatively slow lens means a lot of light (or a flash) is necessary for handheld photos. Handholding a slow lens at 300mm requires a lot of light to begin with. IS comes to the rescue here if your subject is not moving fast.
Some pincushioning is visible at 300mm.
Focus speed is OK, but not fast. Micro USM (Ultrasonic Motor) is not as fast as Canon's excellent Ring USM. FTM (Full-Time Manual) focusing is not part of the package. My kids could easily outrun the Canon EF 75-300mm f/4-5.6 IS USM Lens's focusing capabilities even when mounted on a Canon pro camera body.
An 8-bladed aperture is a nice touch. Generally speaking, more aperture blades yield more-round out of focus highlights. Of course, rounded aperture blades are better the straight ones.
From left to right in the comparison picture above are the Canon EF 24-70 f/2.8 L USM Lens, Canon EF 75-300 f/4-5.6 III USM Lens, Canon EF 75-300 f/4-5.6 IS USM Lens and Canon EF 70-200 f/2.8 L IS USM Lens.
Pictured above from left to right are the Canon 24-70mm f/2.8 L USM Lens, the Canon EF 70-300 f/4.5-5.6 DO IS USM Lens, the Canon EF 75-300 f/4-5.6 IS USM Lens and the Canon EF 70-200mm f/2.8 L IS USM Lens.
The Canon EF 75-300mm f/4-5.6 IS USM Lens is mid-sized and not too heavy - it is not a burden to carry. The lens extends and rotates when zooming to 300mm. The rotation is a problem when using a polarizing filter or similar attachment.
The 75-300mm focal length is very useful. A wide variety of uses can be found for this range including portraits/people, pets, nature ...
Price is one of the reasons you might consider this lens. The 75-300 IS is very capable of capturing memories.
My recommendation - for a little more money, you can get the Canon EF 70-200 f/4 L Lens. The image and build quality of this lens are much better. Even with a Canon Extender 1.4x II attached, my 70-200 L lens resulted in better image quality than the Canon EF 75-300mm f/4-5.6 IS USM Lens alone.
If you care about excellent quality, sharp photos, the Canon EF 75-300mm f/4-5.6 IS USM Lens is not for you. And Photoshop cannot enhance details that are not there. If your needs are not demanding, you might be very happy with a 75-300 IS.