It's good that it's free with ads, no credit card required, but I wasn't impressed with the quality of the upscale.

Google Slides offers more precise control. It's slower to crank out a presentation though, no generation from an outline for instance.

Makes it easy to get started with a presentation if you have an outline, but as soon as you want more control, you're better off using Google Slides. Gamma's feature that I used the most was image generation - you can select among a variety of models (Ideogram, Flux, DALL-E, but not Midjourney), and it shows 3 variations to choose from. Performance is slow and a little janky, even in Chrome. Prompts and settings are often not respected - e.g. you set it to "preserve text" and just generate slides, and it goes onto dumping an entire 3 paragraphs of text in one slide. You can't overlay text over images (e.g. for image attribution), and there's no precise positioning control, or grouping elements. No way to control table layout, e.g. to have two images slide-by-side in full bleed mode. I tried Gamma for a new presentation, but next time I need to make a presentation, I'll go back to Google Slides and generate images independently.