Jurassic Life, a mod for Half-Life 2 is released as a separate game, so you can play it without having to buy HL2. You will need the SOURCE SDK 2013, which you can get for free. 

As the team noted, this free game will only require SOURCE SDK 2013 (which you can get from Steam). Moreover, the team will share the official PC system requirements for this free Jurassic Park game soon:

The Jurassic Life team has also released a new video. This video features 10 minutes of in-game footage. The video introduces us the primary system of tools and arms. Additionally, the team plans to release a second video that will give you a proper tour of the park.

Now as you will see from some brief gameplay sequences, Jurassic Life is a bit rough around the edges. However, you should keep in mind that this is an indie free game and not an official triple-A Jurassic Park game. As such, I believe should focus on the positive things of this fan game.

In Jurassic Life, you play game warden Robert Muldoon who was hired to keep order in the quite extraordinary Jurassic Park, located on Isla Nublar. Do note that its story is not strictly based on the movies or novels. Instead, this is a new tale that takes inspiration from the world of Jurassic Park. However, the team describes it as a side story which includes several scenes from the original film. As such, the story plays out at the timeframe seen in the first movie. Enjoy the following video and stay tuned for more.

The game will be available this year (without a specific date for its release) and will be completely free.