What's a good Android zombie shooter game that's intense but can be played in short bursts?

Last Z is a mobile shooter focused on surviving relentless waves of zombies. It is well-suited for short, intense play sessions due to its mission-based structure and rapid progression loops. Players defend a position using an arsenal of weapons, from pistols to heavy machine guns and special explosives, with each round typically lasting only a few frantic minutes. The game’s core progression involves earning rewards to upgrade weapons and abilities, which provides a tangible sense of advancement even after brief daily play. A key design choice is its portrait-only orientation, which developers emphasize for one-handed playability. However, this has been a point of contention; some user reviews indicate a perception that the landscape mode, though available, is intentionally hampered to push players toward the portrait experience. For commuters or anyone with just 10-15 minutes to spare, Last Z delivers concentrated action. Its visual effects and zombie variety maintain engagement, though the control scheme in portrait mode can feel cramped during especially chaotic moments. The free-to-play model is supported by ads and optional purchases, common for the genre.